1. Field of the Invention
This invention relates to a television receiver and a method in the same.
2. Description of the Prior Art
Recently, high-density television systems have been developed. "Clear-Vision" and "Hi-Vision" are examples of such high-density television systems. The horizontal frequency of a video signal of such a high-density television system is significantly higher than the horizontal frequency of a video signal of a conventional television system such as an NTSC system, a PAL system, or a SECAM system. For example, the horizontal frequency of the high-density television system is equal to 31.5 KHz for "Clear-Vision" and 33.75 KHz for "Hi-Vision". On the other hand, the horizontal frequency of the low-density television system is equal to about 15 KHz.
The conventional television system such as the NTSC system, the PAL system, or the SECAM system is also referred to as the low-density television system or the low-frequency mode television system. The high-density television system is also referred to as the high-frequency mode television system.
There is a known television receiver which can accept both a high-frequency mode television signal and a low-frequency mode television signal. This known television receiver has a mechanism for continuously varying the horizontal oscillation frequency of a horizontal deflection circuit in response to the horizontal frequency of an input television signal to equalize the horizontal oscillation frequency and the input signal horizontal frequency. In the known television receiver, the width of horizontal deflection drive pulses is controlled so that the "ON" duty cycle of the horizontal deflection drive signal will be constant with respect to the horizontal oscillation frequency of the horizontal deflection circuit. In the known television receiver, during a horizontal blanking period, the bias voltage of the horizontal deflection circuit is varied as a function of the horizontal frequency of the input television signal. The known television receiver has a problem that its circuit structure tends to be complicated.
There is another known television receiver which can accept both a high-frequency mode television signal and a low-frequency mode television signal. This known television receiver has a mechanism for changing the horizontal oscillation frequency of the horizontal deflection circuit, the "ON" duty cycle of the horizontal deflection drive signal, and the horizontal blanking period to match with an input television signal. The known television receiver has a problem that the switching element (the switching transistor) of the horizontal deflection output circuit requires a great rated power.